Protective sleeve for spark plug

ABSTRACT

A protective sleeve for a spark plug includes a center electrode, an insulator, an attachment fitment having an attachment screw section formed on an outer peripheral surface thereof, and a ground electrode. A protective sleeve is disposed in a detachable manner on the outer periphery of the attachment screw section. The attachment fitment includes a flange section that has a diameter larger than that of the attachment screw section on a base end side of the attachment screw section. The protective sleeve includes a main body cylinder section having an inner diameter that is the diameter of the attachment screw section or larger, and smaller than the diameter of the flange section, a large diameter cylinder section having an inner diameter that is the diameter of the flange section or larger, and a step section formed between the large diameter cylinder section and the main body cylinder section.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority from earlier Japanese Patent Applications No. 2011-64792 filed Mar. 23, 2011, and No. 2012-24373 filed Feb. 7, 2012, the descriptions of which are incorporated herein by references.

TECHNICAL FIELD

The present disclosure relates to a protective sleeve for a spark plug used as an igniting means in a combustion chamber of an internal combustion engine, such as an automobile engine.

BACKGROUND

In an internal combustion engine, such as an automobile engine, a spark plug is attached to the interior of the engine by an attachment screw section being screwed into a female screw section (refer to Japanese Patent Application Laid-Open Publication No. 11-324878). The female screw section is formed in a plug attachment hole formed in a cylinder head. The attachment screw section is formed on the tip side of an attachment fitment of the spark plug.

In addition, as shown in FIG. 21, a spark plug 9, described above, has a center electrode 92, an insulator 93, an attachment fitment 94, and a ground electrode 95. The center electrode 92 is held within the insulator 93. The insulator 93 is held within the attachment fitment 94. The attachment fitment 94 is configured such that an attachment screw section 941 that is screwed into the internal combustion engine is formed on the outer peripheral surface thereof. A spark discharge gap is formed between the center electrode 92 and the ground electrode 95.

Furthermore, the attachment fitment 94 has a flange section 942 formed on the base end side of the attachment screw section 941.

Due to rising crude oil prices, increasing concern for global warming, and the like, alcohol fuels, in addition to gasoline, are being more frequently used in recent years as fuel for internal combustion engines such as automobile engines. Alcohol fuels produce a large amount of moisture during combustion, and produce large quantities of acidic compounds, such as formic acid and nitric acid. Therefore, the attachment screw section that attaches the spark plug to the female screw section of the cylinder head becomes corroded as a result of deposits of acids, described above. Iron rust accumulates in the space between the attachment screw section and the female screw section.

Therefore, when the spark plug is removed from the cylinder head to replace the spark plug, the iron rust clogs the space. As a result, the attachment screw section of the spark plug may become stuck to the internal combustion engine. Removal of the spark plug from the cylinder head may become difficult.

Therefore, to prevent sticking, the outer peripheral surface of the attachment screw section may be coated with grease. However, in this instance, the grease adheres to, for example, the hands of an operator or a jig during transport, assembly, and the like of the spark plug. As a result, the required amount of grease may not be provided. In addition, a problem occurs in that dust and the like become easily attached to the attachment screw section.

Furthermore, the center electrode and the ground electrode configuring the spark discharge gap are adjusted with high precision. Therefore, protection of the center electrode and the ground electrode during transport and handling of the spark plug is also demanded.

Therefore, as shown in FIG. 22, attaching a protective sleeve 96 to the outer periphery of the attachment screw section 941 and the spark discharge gap is being considered.

The shape of the protective sleeve 96 is, for example, a circular cylinder having an inner diameter that is almost the same as the diameter of the attachment screw section 941, as shown in FIG. 22. As a result, the protective sleeve 96 can be fitted onto the attachment screw section 941.

However, during assembly of the spark plug 9, the protective sleeve 96 is required to be removed from the spark plug 9 by the operator by hand, using a jig, or the like. Alternatively, the protective sleeve 96 is removed by a robot or the like. Therefore, when the protective sleeve 96 has a circular cylindrical shape as described above, the outer peripheral surface of the protective sleeve 96 is required to be gripped. An issue occurs in that removal is difficult. In particular, when removal by a robot is required, this issue may significantly affect production efficiency.

Therefore, from the perspective of improving removal operability of the protective sleeve 96, the following can be considered. As shown in FIG. 23, the inner diameter of the protective sleeve 96 is set to be greater than the diameter of the flange section 942 of the attachment fitment 94. The protective sleeve 96 is fitted onto the flange section 942. As a result, the gripping section of the robot or the like can be hooked to the end surface 960 on the base end side of the protective sleeve 96, thereby facilitating removal of the protective sleeve 96. However, in this instance, the positioning in the axial direction of the protective sleeve 96 in relation to the spark plug 9 cannot be performed. Mounting the protective sleeve 96 in an accurate position becomes difficult. In other words, a mounting state in which the function of the protective sleeve 96, described above, cannot be achieved occurs more easily.

SUMMARY

An embodiment provides a protective sleeve for a spark plug that can be easily mounted in a suitable position in relation to a spark plug and can be easily removed from the spark plug.

In a protective sleeve for a spark according to a first aspect, the protective sleeve for a spark plug includes a center electrode, an insulator holding the center electrode therein, an attachment fitment holding the insulator therein and configured such that an attachment screw section that is screwed into an internal combustion engine is formed on an outer peripheral surface thereof, and a ground electrode that forms a spark discharge gap with the center electrode.

The protective sleeve is disposed in a detachable manner on the outer periphery of the attachment screw section.

The attachment fitment includes a flange section on a base end side of the attachment screw section.

The flange section has a diameter that is larger than that of the attachment screw section.

The protective sleeve includes a main body cylinder section having an inner diameter that is the diameter of the attachment screw section or larger, and smaller than the diameter of the flange section, a large diameter cylinder section having an inner diameter that is the diameter of the flange section or larger, and a step section formed between the large diameter cylinder section and the main body cylinder section.

The protective sleeve for a spark plug of the present disclosure includes the main body cylinder section, the large diameter cylinder section, and the step section. As a result, the protective sleeve can be mounted onto the spark plug such that the large diameter cylinder section is positioned on the outer periphery of the flange section, and the main body cylinder section is positioned on the outer periphery of the attachment screw section. At this time, the step section can be in direct or indirect contact with the flange section. Therefore, the protective sleeve can be positioned in the axial direction in relation to the attachment screw section of the spark plug. The protective sleeve can be easily mounted in a suitable position.

In addition, in a state in which the protective sleeve is mounted onto the spark plug, the large diameter cylinder section is positioned on the outer periphery of the flange section. Therefore, when the protective sleeve is removed from the spark plug, a jig or the like can be hooked onto an end surface of the large diameter cylinder section that is the end surface on the base end side of the protective sleeve. As a result, the protective sleeve can be easily removed.

As described above, as a result of the present invention, a protective sleeve for a spark plug that can be easily mounted in a suitable position in relation to a spark plug and can be easily removed from the spark plug can be provided.

The above-described main body cylinder section is preferably configured such as to be also disposed in the outer peripheries of the center electrode and the ground electrode. In this instance, the center electrode and the ground electrode that configure the spark discharge gap and are adjusted with high precision can be protected reliably during transport and handling of the spark plug.

In the protective sleeve for a spark according to a second aspect, the large diameter cylinder section is configured to be fitted onto the flange section.

In the protective sleeve for a spark according to a third aspect, the protective sleeve is configured such as to cover a coating that coats the attachment screw section, and a coating pool in which the coating accumulates is formed on the inner side of the step section and the large diameter cylinder section when the protective sleeve is mounted onto the outer periphery of the attachment screw section.

The coating preferably has conductivity. In this instance, should the coating leak from the protective sleeve and adhere to, for example, the center electrode, the ground electrode, or to peripheral electronic components via the hands of an operator, a jig, or the like, problems such as short-circuiting occur. Therefore, as described above, it is very important that the protective sleeve is configured to prevent leakage of the coating.

The spark plug is preferably used in an internal combustion engine that uses an alcohol fuel. In this instance, the conditions of use tend to cause the spark plug to stick to the internal combustion engine. Therefore, the outer periphery of the attachment screw section is required to be coated with grease or the like. Thus, as described above, it is very important that the protective sleeve is configured to prevent leakage of the coating.

In addition, the side of the spark plug that is inserted into the combustion chamber of the internal combustion engine is referred to as a tip side in the description. The other side is referred to as a base end side.

In the protective sleeve for a spark according to a fourth aspect, a tilt angle of the step section in relation to an axial direction of the protective sleeve is 45 degrees or less.

In the protective sleeve for a spark according to a fifth aspect, a thickness of the large diameter cylinder section is greater than a thickness of the main body cylinder section.

In the protective sleeve for a spark according to a sixth aspect, the large diameter cylinder section has a shoulder surface facing a tip side in an axial-direction, further from the outer peripheral side than to the step section.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an explanatory, partially cross-sectional side view of a spark plug on which a protective sleeve is mounted in a first example;

FIG. 2 is a side view of the protective sleeve in the first example;

FIG. 3 is a top view of the protective sleeve in the first example;

FIG. 4 is a cross-sectional view taken along line A-A in FIG. 3;

FIG. 5A to FIG. 5D are explanatory, partially cross-sectional side views of a mounting process of the protective sleeve in the first example;

FIG. 6 is an explanatory, cross-sectional side view of a coating pool of the protective sleeve in the first example;

FIG. 7A to FIG. 7D are explanatory, partially cross-sectional side views of a mounting process of a protective sleeve in a comparison example:

FIG. 8 is a side view of the protective sleeve in a second example;

FIG. 9 is a top view of the protective sleeve in the second example;

FIG. 10 is a cross-sectional view taken along line B-B in FIG. 9;

FIG. 11 is a vertical cross-sectional view of a protective sleeve in a third example;

FIG. 12 is a top view of the protective sleeve in the third example;

FIG. 13 is an explanatory diagram of a state in which a spark plug on which a protective sleeve is mounted is placed on a packaging material;

FIG. 14 is an explanatory diagram of a state in which a protective sleeve that does not have a shoulder surface is fitted into a recess section of the packaging material;

FIG. 15 is an explanatory diagram of a state in which the protective sleeve that does not have a shoulder surface deforms a portion of the packaging material;

FIG. 16 is an explanatory diagram of when a robot pulls out the spark plug on which the protective sleeve is mounted from the packaging material in the third example;

FIG. 17 is an explanatory diagram of a state in which the spark plug on which the protective sleeve is mounted is held in a mounting machine in the third example;

FIG. 18 is a vertical cross-sectional view of a protective sleeve in a fourth example;

FIG. 19 is an explanatory diagram of a state in which a spark plug on which a protective sleeve is mounted is placed on a packaging material in the fourth example

FIG. 20 is an explanatory diagram of a state in which the spark plug on which a protective sleeve is mounted is packaged by a pair of packaging materials in the fourth example;

FIG. 21 is a side view of a spark plug of a conventional technology;

FIG. 22 is an explanatory, partially cross-sectional side view of a protective sleeve fitted onto an attachment screw section in the conventional technology;

FIG. 23 is an explanatory, partially cross-sectional side view of a protective sleeve fitted onto a flange section in the conventional technology.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Example

A protective sleeve 1 of an example of the present disclosure will be described with reference to FIG. 1 to FIG. 4.

As shown in FIG. 1, the protective sleeve 1 of a first example is disposed in a detachable manner on the outer periphery of an attachment screw section 41 in a spark plug 6 for an internal combustion engine.

The spark plug 6 includes a center electrode 2, an insulator 3, an attachment fitment 4, and a ground electrode 5. The center electrode 2 is held within the insulator 3. The insulator 3 is held within the attachment fitment 4. The attachment fitment 4 is configured such that an attachment screw section 41 that is screwed into the internal combustion engine is formed on the outer peripheral surface thereof. A spark discharge gap is formed between the center electrode 2 and the ground electrode 5.

The attachment fitment 4 has a flange section 42 formed on the base end side of the attachment screw section 41. The diameter of the flange section 42 is larger than that of the attachment screw section 41.

As shown in FIG. 1 to FIG. 4, the protective sleeve 1 includes a main body cylinder section 11, a large diameter cylinder section 12, and a step section 13. The main body cylinder section 11 has an inner diameter that is the diameter of the attachment screw section 41 or larger, and smaller than the diameter of the flange section 42. The large diameter cylinder section 12 has an inner diameter that is the diameter of the flange section 42 or larger. The step section 13 is formed between the large diameter cylinder section 12 and the main body cylinder section 11.

In addition, the large diameter cylinder section 12 is configured to be fitted onto the flange section 42. In other words, in the first example, the inner diameter of the large diameter cylinder section 12 is formed to be substantially equivalent to the diameter of the flange section 42. The outer shape of the flange section 42 and the inner shape of the large diameter cylinder section 12 are formed such that a cross-section perpendicular to the axial direction is substantially circular. In other words, the cross-section perpendicular to the axial direction of the flange section 42 is formed into a substantially circular shape. To match this outer shape, the large diameter cylinder section 12 is formed into a circular cylindrical shape as shown in FIG. 3.

As shown in FIG. 1 and FIG. 4, the step section 13 is formed into a tapered shape between the main body cylinder section 11 and the large diameter cylinder section 12. The step section 13 has a tilt angle α of 45 degrees or less in relation to the axial direction of the protective sleeve 1.

The protective sleeve 1 is integrally molded using polypropylene (PP). However, the material of the protective sleeve 1 is not particularly limited as long as the material is not dissolved by oil, and the large diameter cylinder section and the step section 13 can be elastically deformed. Therefore, for example, the protective sleeve 1 may be molded using polyethylene terephthalate (PET), silicon, or the like.

Next, a method of mounting the protective sleeve 1 of the first example on the spark plug 6 and a method of removing the protective sleeve 1 from the spark plug 6 will be described with reference to FIG. 5A and FIG. 6.

A coating 7 is applied to the outer periphery of the attachment screw section 41 of the spark plug 6. As the coating 7, for example, conductive grease containing metal particles is used. However, the coating 7 is not limited thereto.

First, as shown in FIG. 5A and FIG. 5B, a predetermined amount of the coating 7 is applied to the outer periphery on the tip side of the attachment screw section 41 of the spark plug 6. Next, as shown in FIG. 5C, the protective sleeve 1 is fitted in the axial direction in relation to the attachment fitment 4, from the tip side of the spark plug 6. As a result, the large diameter cylinder section 12 is fitted onto the flange section 42. At this time, the coating 7 is spread by the inner peripheral surface of the main body cylinder section 11 and applied to the overall outer peripheral surface of the attachment screw section 41.

Here, in the process of fitting the protective sleeve 1 onto the attachment fitment 4, the coating 7 first comes into contact with the step section 13. The step section 13 pushes and spreads some of the coating 7 over the outer peripheral surface of the attachment screw section 41 towards the base end side. On the other hand, the remaining coating 7 enters between the main body cylinder section 11 and the attachment screw section 41 from the step section 13. As a result, the coating 7 coats the outer peripheral surface of the attachment screw section 41. As described above, the tilt angle α of the step section 13 in relation to the axial direction of the protective sleeve 1 is 45 degrees or less. Therefore, the coating 7 can smoothly enter from the inner side of the step section 13 into the inner side of the main body cylinder section 11. As a result, the coating 7 is easily applied to the overall attachment screw section 41. In addition, the operation of mounting the protective sleeve 1 onto the attachment screw section 41 can be smoothly performed.

In other words, when the spark plug 6 is inserted into the protective sleeve 1, first, the coating 7 is temporarily collected in an area surrounded by the step section 13 of the protective sleeve 1 and the attachment screw section 41, the flange section 42, and a sealing material 43 of the spark plug 6. The coating 7 then enters inside the main body cylinder section 11 such as to be dragged by the attachment screw section 41. However, when the tilt angle α of the step section 13 exceeds 45 degrees, the coating 7 cannot smoothly enter inside the cylinder section 11. The coating 7 tends to back-flow towards a gap between the flange section 42 of the spark plug 6 and the large diameter cylinder section 12 shown in FIG. 6. The coating 7 may leak out from the gap between the flange section 42 and the large diameter cylinder section 12. In this instance, an issue occurs in that the leaked coating 7 adheres to the hands of a person performing the attachment operation of the protective sleeve 1 and soils other sections, or the like. This issue can be more easily controlled by reducing the tilt angle α of the step section 13 and securing a space for pooling the coating 7. From this perspective, the tilt angle α is preferably 45 degrees or less.

However, when the tilt angle α is too small, the function of the step section 13, which is to position the protective sleeve 1 and the spark plug 6 in the axial direction, may decrease. From this perspective, in the first example, the tilt angle α is preferably 30 degrees or more.

As a result of the above, the tilt angle α is preferably 30 degrees to 45 degrees.

In addition, as shown in FIG. 6, in the state in which the protective sleeve 1 is mounted onto the attachment screw section 41, the step section 13 is in indirect contact with the flange section 42. In other words, the step section 13 is in contact with the flange section 42 with the coating 7 therebetween. As a result, the main body cylinder section 11 is positioned in relation to the axial direction of the attachment fitment 4 and is positioned on the outer periphery of the attachment screw section 41.

The spark plug 6 is configured such that the metal ring-shaped sealing material 43 is disposed on the surface on the tip side of the flange section 42. The coating 7 is interposed between the sealing material 43 and the step section 13 as well. In this state, the protective sleeve 1 is disposed such as to cover the coating 7 that coats the attachment screw section 41. A coating pool 14 in which the coating 7 accumulates is formed on the inner side of the step section 13 and the large diameter cylinder section 12.

In addition, the tip of the main body cylinder section 11 is disposed further towards the tip side than to the tip of the spark plug 6. In other words, the main body cylinder section is also disposed on the outer peripheries of the center electrode 2 and the ground electrode 5.

As shown in FIG. 5D, when the protective sleeve 1 is removed in the axial direction from the attachment screw section 41, a jig or the like is hooked onto the end surface 120 of the large diameter cylinder section 12. The protective sleeve 1 is slid towards the tip side in relation to the spark plug 6.

Next, operational effects of the protective sleeve 1 of the first example will be described.

The protective sleeve 1 of the first example includes the main body cylinder section 11, the large diameter cylinder section 12, and the step section 13. As a result, the protective sleeve 1 can be mounted onto the spark plug 6 such that the large diameter cylinder section 12 is positioned on the outer periphery of the flange section 42 and the main body cylinder section 11 is positioned on the outer periphery of the attachment screw section 41. At this time, the step section 13 can be in direct or indirect contact with the flange section 42. Therefore, the protective sleeve 1 can be positioned in the axial direction in relation to the attachment screw section 41 of the spark plug 6. The protective cylinder 1 can be easily mounted in a suitable position.

In addition, in the state in which the protective sleeve 1 is mounted onto the spark plug 6, the large diameter cylinder section 12 is positioned on the outer periphery of the flange section 42. Therefore, when the protective sleeve 1 is removed from the spark plug 6, the jig or the like can be hooked onto the end surface 120 of the large diameter cylinder section 12 that is the end surface on the base end side of the protective sleeve 1. Therefore, the protective sleeve 1 can be easily removed.

In addition, the large diameter cylinder section 12 is configured such as to be fitted onto the flange section 42. As a result, the protective sleeve 1 can be mounted onto the attachment fitment 4 with certainty. In addition, when the coating 7 is applied to the attachment screw section 41, the coating 7 can be prevented from leaking from the base end side of the attachment screw section 41. Furthermore, because fitting does not have to be performed by the main body cylinder section 11, clearance between the attachment screw section 41 and the main body cylinder section 11 can be freely set.

In addition, the protective sleeve 1 is configured to be disposed such as to cover the coating 7 applied to the attachment screw section 41. When the protective sleeve 1. is mounted onto the outer periphery of the attachment screw section 41, the coating pool 14 in which the coating 7 accumulates is formed on the inner side of the step section 13 and the large diameter cylinder section 12. As a result, the coating 7 can be effectively prevented from leaking from the base end side of the attachment screw section 41.

As described above, in the first example, a protective sleeve for a spark plug can be provided that can be easily mounted in an accurate position in relation to the spark plug and can be easily removed from the spark plug.

First Comparison Example

A first comparison example is a protective sleeve 10 of which the overall shape is a circular cylinder. In other words, neither the large diameter cylinder section 12 nor the step section 13 is formed in the protective sleeve 10 of the first comparison example.

When the protective sleeve 10 is mounted onto the attachment fitment 4 of the spark plug 6, as shown in FIG. 7A and FIG. 7B, a predetermined amount of coating 7 is applied to the outer periphery on the tip side of the attachment screw section 41 of the spark plug 6. Next, as shown in FIG. 7C, the protective sleeve 10 is fitted in the axial direction in relation to the attachment fitment 4, from the tip side of the spark plug 6. The protective sleeve 10 is fitted onto the attachment screw section 41.

At this time, the coating 7 is spread from the tip side to the base end side of the outer periphery of the attachment screw section 41 by the inner peripheral surface of the protective sleeve 10. The coating 7 coats the overall surface of the outer periphery of the attachment screw section 41. However, as shown in FIG. 7C, as the protective cylinder 10 approaches the flange section 42 of the attachment fitment 4, the coating 7 is pushed outwards by the inner peripheral side of the protective sleeve 10. The coating 7 leaks out from the base end side of the attachment screw section 41.

Then, as shown in FIG. 7D, when the protective sleeve 10 is removed in the axial direction from the attachment screw section 41, because an amount of coating 7 has leaked, an appropriate amount of coating 7 is not likely to be applied to the outer peripheral surface of the attachment screw section 41. Therefore, unless a sufficient amount of coating 7 is applied to the attachment screw section 41, the desired intention of the coating 7, such as to prevent the spark plug 6 from sticking to the internal combustion engine, may be difficult to achieve.

In addition, the coating 7 that has leaked is adhered near the flange section 42. As a result, the coating 7 on the flange section 42 and the like adheres to the hands of the operator, the jig, or the like. Moreover, an issue may occur in which the coating 7 adheres to the spark discharge gap of the spark plug 6, other electronic components, and the like.

In addition, as shown in FIG. 7C, in a state in which the protective sleeve 10 is mounted onto the attachment fitment 4, the base end section of the protective sleeve 10 is in contact with the sealing material 43 disposed on the tip-side surface of the flange section 42. Therefore, as shown in FIG. 7D, when the protective sleeve 10 is removed from the attachment fitment 4, the outer peripheral surface of the protective sleeve 10 is required to be gripped, and the protective sleeve 10 pulled up towards the axial-direction tip side. Therefore, a gripping means (such as hands, a jig, or a robot) easily slips from the protective sleeve 10. Failure in removal of the protective sleeve 10 easily occurs. This may result in decreased production efficiency.

On the other hand, as described above, as a result of the protective sleeve 1 of the first example, leakage of the coating 7, issues such as failure in removal of the protective sleeve 1 from the spark plug 6, and the like, such as those described above, can be prevented.

Second Example

As shown in FIG. 8 to FIG. 10, in a second example, ribs 110 are formed on the inner peripheral surface of the main body cylinder section 11 of the protective sleeve 1.

The ribs 110 are formed on the inner peripheral surface of the main body cylinder section 11, over the overall the main body cylinder section 11 in the axial direction. The ribs 110 are formed by projecting strips raised in a substantially columnar shape. As shown in FIG. 9, the ribs 110 are formed evenly spaced in three areas in the peripheral direction.

However, the number of ribs 110 is not particularly limited. For example, four or more ribs 110 may be formed.

In the second example, from the following perspective, the tilt angle α of the step section 13 (see FIG. 6) is preferably 30 degrees or more. In other words, when the spark plug 6 and the protective sleeve 1 are fixed by the attachment screw section 41 and the main body cylinder section 11 being fitted together as a result of the ribs 110 being provided as in the second example, stable fitting of the attachment screw section 41 and the main body cylinder section 11 may become difficult if the tilt angle α is excessively small. In other words, in the second example, the spark plug 6 is fixed to the protective sleeve 1 as a result of the main body cylinder section 11 and the attachment screw section 41 being fitted together, rather than the large diameter cylinder 12 and the flange section 42 being fitted together. In this instance, when the tilt angle α of the step section 13 is too small, the length of the contacting section between the ribs 110 provided in the main cylinder section 11 and the attachment screw section 41 becomes insufficient. Fixing strength thereof becomes difficult to increase. From this perspective, in the second example, the tilt angle α is preferably 30 degrees or more. Taking this into account with the reason for setting the upper limit value of the preferred tilt angle α described in the first example, the tilt angle α in the second example is preferably 30 degrees to 45 degrees.

The second example is similar to the first example in other aspects. Configurations in the drawings having the same reference numbers as those in the first example are similar to those described in the first example unless otherwise noted.

In the protective sleeve 1 of the second example, the ribs 110 are formed on the inner peripheral surface of the main body cylinder section 11. As a result, sufficient clearance can be formed between the attachment screw section 41 and the main body cylinder section 11. Therefore, the coating 7 can be applied with a sufficient predetermined thickness to the attachment screw section 41.

In addition, operational effects similar to those of the first example are achieved.

In the first example and the second example described above, a configuration is described in which the large diameter cylinder section 12 is fitted onto the flange section 42, and clearance is formed between the main body cylinder section 11 and the attachment screw section 41. However, a configuration is also possible in which the main body cylinder section 11 is fitted onto the attachment screw section 41, and clearance is formed between the large diameter cylinder section 12 and the flange section 42. As a result of this configuration as well, the protective sleeve 1 can be mounted onto the spark plug 6 such that the main body cylinder section 11 is positioned on the outer periphery of the attachment screw section 41, and the large diameter cylinder section 12 is positioned on the outer periphery of the flange section 42.

Third Example

As shown in FIG. 11 to FIG. 13, a third example is a protective sleeve 1 in which the thickness W1 of the large diameter cylinder section 12 is greater than the thickness W3 of the main body cylinder section 11.

In the protective sleeve 1 of the third example, as shown in FIG. 11, the outer diameter of the large diameter cylinder 12 is larger than the maximum outer diameter of the step section 13 formed in a tapered shape between the main body cylinder section 11 and the large diameter cylinder section 12. In other words, the outer diameter of the large diameter cylinder section 12 is larger than the outer diameter of the base end section of the step section 13. The large diameter cylinder section 12 projects outwards in the radial direction from the base end section of the step section 13. As a result, the thickness W1 of the large diameter cylinder section 12 is greater than the thickness W3 of the main body cylinder section 11.

The large diameter cylinder section 12 has a shoulder surface 121 facing the axial-direction tip side, further from the outer peripheral side than to the step section 13. In other words, the shoulder surface 121 is formed on the end surface in the axial direction on the step section 13 side, in the portion of the large diameter cylinder section 12 projecting towards the outer peripheral side. The shoulder surface 121 is formed on the overall outer periphery of the step section 13. In addition, the shoulder section 121 is perpendicular to the axial direction of the protective sleeve 1.

The width W2 of the shoulder surface 121 of the large diameter cylinder section 12 is preferably greater than the thickness W3 of the main body cylinder section 11. In addition, the thickness W1 of the large diameter cylinder section 12 is preferably twice the thickness W3 of the main body cylinder section 11 or greater. Furthermore, the thickness W1 is more preferably three times the thickness W3 or greater.

The protective sleeve 1 is ordinarily disposable. Therefore, the protective sleeve 1 is preferably manufactured at low cost. Thus, materials such as PP are used. However, in this instance, as tradeoff, an issue occurs in that the shape after molding and mold-releasing becomes easily warped. When the warping is significant, the diameter of an inscribed circle of the large diameter cylinder section 12 becomes smaller than the outer diameter of the flange section 42 of the spark plug 6. Force may be required to fit the protective sleeve 1. An issue may occur in that productivity decreases. Therefore, the thickness W1 of the large diameter cylinder 12 is preferably greater than the thickness W3 of the main body cylinder section 11. In particular, when the protective sleeve is fixed by the large diameter cylinder section 12 being fitted onto the flange section 42 as in the third example, the thickness W1 of the large diameter cylinder section 12 is preferably increased as described above.

Functionality is sufficient even when the thickness W3 of the main body cylinder 11 is about 0.5 mm. However, when the thickness W1 of the large diameter cylinder section 12 is set to twice or, more preferably, at least three times the thickness W3 of the main body cylinder section 11, warping can be reduced. A shape that does not impede fitting can be achieved. As a result, mass production of the spark plug 6 in a short amount of time can be supported. The cost of the protective sleeve 1 itself can be reduced.

Furthermore, as a result of the thickness W1 of the large diameter cylinder section 12 being increased as described above, the width W2 of the shoulder surface 121 can be increased as well. Therefore, packaging can also be facilitated, as described hereafter. Numerous functions that are more than simple “protection” can be achieved.

On the other hand, a more compact packaging can be actualized; the smaller the pitch is between spark plugs 6 during packaging. Compact packaging is preferable in terms of transport cost. Therefore, excessively increasing the width W2 of the shoulder surface 121 of the large diameter cylinder section 12 of the protective sleeve 1 is not desirable. In other words, excessively increasing the thickness W1 of the large diameter cylinder section 12 in relation to the thickness W3 of the main body cylinder section 11 is not desirable. For practical use, the thickness W1 is ideally about three times the thickness W3.

As shown in FIG. 11 and FIG. 12, a plurality of ribs 122 are formed on the inner peripheral surface of the large diameter cylinder section 12, over the overall large diameter cylinder section 11 in the axial direction. The ribs 122 are formed by projecting pieces raised in a substantially semi-columnar shape. The ribs 122 are formed evenly spaced in three areas in the peripheral direction. However, the number of ribs 122 and the like are not particularly limited.

In addition, in the third example, the ribs 110 such as those provided in the protective sleeve 1 of the second example (see FIG. 8 to FIG. 10) are not formed on the inner peripheral surface of the main body cylinder section 11.

The protective sleeve 1 of the third example is configured to be fitted in the large diameter cylinder section 12 such that the ribs 122 come into contact with the flange section 42 of the spark plug 6.

The third example is similar to the first example in other aspects. Configurations in the drawings having the same reference numbers as those in the first example are similar to those described in the first example unless otherwise noted.

Next, operational effects of the third example will be described.

In the protective sleeve 1 of the third example, the following operational effects can be achieved as a result of the shoulder surface 121 being provided.

In other words, as shown in FIG. 13, the spark plug 6 on which the protective sleeve 1 is mounted is transported and stored in a state in which the spark plug 6 is housed in a packaging material 71 composed of polystyrene foam or the like. In other words, the spark plug 6 on which the protective sleeve 1 is mounted is erected in a recess section 711 formed in the packaging material 71, such as to be inserted from the tip side in the axial direction.

When the spark plug 6 is disposed in the package member 71 in this way, the shoulder surface 121 of the large diameter cylinder section 12 of the protective sleeve 1 is placed on the package member 71 by coming into contact with the periphery of the opening end of the recess section 711 of the package member 71. This is actualized by the diameter of the recess section 711 being slightly smaller than the diameter of the large diameter cylinder section 12.

However, even when the diameter of the recess section 711 is slightly smaller than the diameter of the large diameter cylinder section 12, unless the shoulder surface 121 is provided in the protective sleeve 1, the large diameter cylinder section 12 may become embedded in the recess section 711, as shown in FIG. 14. Alternatively, as shown in FIG. 15, the step section 13 of the protective sleeve 1 may deform the package member 71 in the periphery of the recess section 711 and become wedged therein. In this instance, when the spark plug 6 is being removed from the package member 71 and assembled to an engine or the like, excessive removing load may be applied. When the spark plug 6 is removed by a robot or the like in this instance, the robot may stop because of an error or the like. As a result, productivity may decrease.

On the other hand, when the protective sleeve 1 including the shoulder surface 121 of the large diameter cylinder section 12 is used, the protective sleeve 1 mounted onto the spark plug 6 does not become embedded in the package member 71. The spark plug 6 can be smoothly removed from the package member 71. For example, as shown in FIG. 16, when the spark plug 6 is removed from the package member 71 by a chuck section 72 of the robot, removal load can be prevented from being applied and the spark plug 6 can be smoothly removed.

In addition, because the thickness W1 of the large diameter cylinder section 12 is large, rigidity of the large diameter cylinder section 12 can be improved. Therefore, when the protective sleeve 1 is removed from the spark plug 6 by the large diameter cylinder section 12 being gripped while fingers or the like are hooked onto the end surface 121 of the large diameter cylinder section 12, the large diameter cylinder section 12 does not easily deform. As a result, the protective sleeve 1 can be smoothly removed from the spark plug 6.

The protective sleeve 1 may be removed from the spark plug 6 by the main body cylinder section 11 being grasped. In this instance, as a result of the ribs 122 being provided on the inner peripheral surface of the large diameter cylinder section 12 and not on the inner peripheral surface of the main body cylinder section 11 as in the third example, removal operation can be more smoothly performed. In other words, when the ribs are formed on the inner peripheral surface of the main body cylinder section 11, the ribs may become wedged in the attachment screw section 41 of the spark plug 6 when the main body cylinder section 11 is gripped with excessive force. Smooth removal of the protective sleeve 1 may be inhibited. However, when the ribs 122 are formed on the inner peripheral surface of the large diameter cylinder section 12, smooth removal operation of the protective sleeve 1, such as that described above, is not inhibited.

For example, when the spark plug 6 is held by a magnet 731 in a mounting machine 73 for mounting the spark plug 6 in an engine or the like, actualizing smooth removal of the protective sleeve 1 as described above is particularly important in terms of productivity. In other words, the force for holding the spark plug 6 of the magnet 731 of the mounting machine 73 is not very large. Therefore, when the protective sleeve 1 is removed from the spark plug 6 in a state in which the magnet 731 is holding the spark plug 6, should the protective sleeve 1 get caught on the attachment screw section 41, the spark plug 6 may also detach from the mounting machine 73. If the protective cylinder 1 can be smoothly removed from the spark plug 1, detachment of the spark plug 6 such as this can be prevented.

In addition, operational effects similar to those of the first example are achieved.

Fourth Example

As shown in FIG. 18 to FIG. 20, a fourth example is a protective sleeve 1 in which the shoulder surface 121 of the large diameter cylinder section 12 recedes further towards the base end side (the side opposite to the main body cylinder section 11 side) than the base end section of the step section 13.

In other words, as shown in FIG. 18, the large diameter cylinder section 12 has two steps of thickness: a thick section 123 and a thin section 124. The thick section 123 is formed closer to the base end side than to the shoulder surface 121. The thin section 124 is thinner than the thick section 123. The thin section 124 is merely required to be thin in relation to the thick section 123. For example, the thickness of the thin section 124 is equivalent to the thickness of the main body cylinder section 11.

The fourth example is similar to the third example in other aspects. Configurations in the drawings having the same reference numbers as those in the third example are similar to those described in the third example unless otherwise noted.

As shown in FIG. 19, in the fourth example, the spark plug 6 on which the protective sleeve 1 is mounted can be stably housed in the packaging material 71. In other words, when the spark plug 6 on which the protective sleeve 1 is mounted is disposed in the packaging material 71, the outer peripheral surface of the thin section 124 of the large diameter cylinder section 12 is disposed within the recess section 711 of the packaging material 71. The shoulder surface 121 of the large diameter cylinder section 12 is placed in the periphery of the opening end of the recess section 711 of the packaging material 71. Therefore, the spark plug 6 on which the protective sleeve 1 is mounted can be stably housed in the packaging material 71 without becoming embedded or wedged in the packaging material 71. As a result, the spark plug 6 housed in the packaging material 71 can be prevented from being jostled by shaking and impact during transport and the like. Problems such as deformation of the ground electrode 5 and the like can be prevented with certainty.

In addition, as shown in FIG. 20, when an upper packaging material 710 covers the lower packaging material 71 in which the spark plug 6 is placed, the thick section 123 of the large diameter cylinder section 12 can be sandwiched in the axial direction by the lower packaging material 71 and the upper packaging material 710. As a result, the spark plug 6 is fixed in the axial direction as well, by the packaging materials 71 and 710. A more stable packaging can be actualized.

In addition, operational effects similar to those of the third example can be achieved.

The packaging materials 71 and 710 shown in FIG. 13 to FIG. 16, FIG. 19, and FIG. 20 have a plurality of recess sections 711 and are capable of holding a plurality of spark plugs 6. However, the packaging materials 71 and 710 are not particularly limited thereto. In FIG. 19 and FIG. 20, two spark plugs 6 held in the packaging materials 71 and 710 are shown. In FIG. 13 to FIG. 16, one spark plug 6 held in the packaging material 71 is shown. However, this is merely for simplicity. Functions and effects do not particularly differ regardless of the number of spark plugs 6.

In the first to third examples, a configuration is described in which the coating 7 is applied to the attachment screw section 41 of the spark plug 6. However, the protective sleeve 1 may be mounted without the coating 7 being applied to the outer periphery of the attachment screw section 41.

In addition, a slit cut in the axial direction may be formed in the large diameter cylinder section 12 to facilitate elastic deformation of the large diameter cylinder section 12.

Furthermore, the protective sleeve 1 may be configured such that a pair of divided protective sleeves is combined in a detachable manner. The shape of the divided protective sleeves is that of the protective sleeve 1 in the first to third examples segmented on a plane including the center axis. In this instance, when the protective sleeve 1 is mounted onto the attachment fitment 4 of the spark plug 6, the pair of divided protective sleeves can be mounted such as to sandwich the attachment screw section 41 of the attachment fitment 4 from the side. The pair of divided protective sleeves can then be assembled.

In addition, the shape of the large diameter cylinder section 12 is not particularly limited as long as the large diameter cylinder section 12 can be fitted onto the flange section 42. Therefore, for example, when the shape of the flange section 42 is such that the cross-section perpendicular to the axial direction is polygonal, the shape of the large diameter section 12 may be a polygonal cylinder to match the shape of the flange section 42. 

1. A protective sleeve for a spark plug comprising: a center electrode; an insulator holding the center electrode therein; an attachment fitment holding the insulator therein and configured such that an attachment screw section that is screwed into an internal combustion engine is formed on an outer peripheral surface thereof; and a ground electrode that forms a spark discharge gap with the center electrode; wherein, a protective sleeve is disposed in a detachable manner on the outer periphery of the attachment screw section, the attachment fitment includes a flange section on a base end side of the attachment screw section, the flange section has a diameter that is larger than that of the attachment screw section, the protective sleeve includes a main body cylinder section having an inner diameter that is the diameter of the attachment screw section or larger, and smaller than the diameter of the flange section, a large diameter cylinder section having an inner diameter that is the diameter of the flange section or larger; and a step section formed between the large diameter cylinder section and the main body cylinder section.
 2. The protective sleeve for the spark plug according to claim 1, wherein, the large diameter cylinder section is configured to be fitted onto the flange section.
 3. The protective sleeve for the spark plug according to claim 1, wherein, the protective sleeve is configured such as to cover a coating that coats the attachment screw section, and a coating pool in which the coating accumulates is formed on the inner side of the step section and the large diameter cylinder section when the protective sleeve is mounted onto the outer periphery of the attachment screw section.
 4. The protective sleeve for the spark plug according to claim 1, wherein, a tilt angle of the step section in relation to an axial direction of the protective sleeve is 45 degrees or less.
 5. The protective sleeve for the spark plug according to claim 1, wherein, a thickness of the large diameter cylinder section is greater than a thickness of the main body cylinder section.
 6. The protective sleeve for the spark plug according to claim 1, wherein, the large diameter cylinder section has a shoulder surface facing a tip side in an axial-direction, further from the outer peripheral side than to the step section. 